The present invention relates to a compressed-air processing system having, in a housing, an electromechanical pressure regulator, preferably an air dryer cartridge, and a multicircuit safety valve having at least one load circuit connected to it. Each load circuit can be locked separately by means of an assigned pressure control unit.
Compressed-air processing systems of known construction utilize compressed air provided by air compressors for operation of pneumatic service brakes, of parking brakes, of other compressed-air operated consuming devices as well as, more recently, of pneumatic suspensions, particularly in utility vehicles. Electronically controlled compressed-air processing systems are used to control rapidly operable solenoid valves according to presettable parameters. Because of the susceptibility of the electronic system and the unavailability of the motor vehicle connected with malfunctioning, it is desirable that the compressed-air processing system function also when the electronic system is failing.
German Patent Document DE-OS 195 15 895 A1 shows a compressed-air procuring arrangement having a compressed-air processing system which feeds compressed air supplied by a compressor by way of an air dryer to a four-circuit safety valve, the valve members of the four-circuit safety valve being controllable by way of assigned pilot valves. The pilot valves of a pressure regulator unit are controlled by a central electronic unit which reacts to the pressure detected by-a pressure sensor in a service brake circuit. The compressed air for the pressure regulator unit and the pneumatic control of the valve members of the four-circuit safety we valve is selectively taken from the service brake circuit or from the delivery pipe behind the air dryer. In the event of failure of the service brake circuit, the valve members must be supplied with control pressure exclusively from the delivery pipe of the pressure regulator. Consequently, a permanent load movement of the compressor is required, and compressor damage can occur much more rapidly because the compressor must permanently deliver against the safety valve pressure and, therefore, is at a risk of overheating. Another inadequacy of the known arrangement is that, in the event of the permanent delivery, the air dryer cartridge will not become pressureless and therefore is no longer regenerated. After a certain time has passed, humidity can penetrate into the brake circuits. Finally, the air dryer is also not regenerated in a controlled manner as a function of the detected air humidity, but, in the case of each electronically triggered pressure compensation between two brake circuits, air flows out permanently by way of a fixedly installed bypass. As a result, the volume to be delivered and the corresponding energy consumption are increased.
European Patent Document, EP-OS 0 830 997 A2 describes an energy supply arrangement for an air brake system of vehicles, in the case of which the pressure control units assigned to-one brake circuit respectively are switched by way of pilot valves which can be controlled by an electric control unit, and in the case of which a cascade-type presetting of the closing pressure of the pressure control units permits a successive filling of the brake circuits in the zero-current operation in the cascade sequence. Also, in this air brake system, compressor damage may occur in the zero-current operation, and a regeneration of an air dryer cartridge is not provided. The access to the brake circuit of the spring brake system takes place by way of an on/off shut-off valve only when a minimum pressure has been built up in the service brake circuits. This on/off shut-off valve permits no regulating or controlling of the pressure.
German Patent Document DE-PS 195 44 621 C1 shows a compressed-air procuring arrangement having a compressed air processing system which has an air dryer, a pressure regulator and a multicircuit safety valve with connected load circuits with electronically controllable overflow valves which shut the circuits off. Because the air suspension results from the same approach flow space from which the load circuits also originate, it is not possible to supply the air suspension with a higher pressure than the brake circuits. Furthermore, it is not possible to continue to operate the pressure regulator pilot control in the zero-current operation. In the zero-current operation, it is also not possible to regenerate the air dryer cartridge. It also should be noted that a fairly long time goes by for the shutting-off of the overflow valves because a large switching volume is required. As a result, the possibility is eliminated of sensitive ventilation in the circuits with a lacking storage tank (in practice, for example, the circuit for the service brake system), which may result in overcontrolling.
It is an object of the invention to provide a compressed-air processing system of the type mentioned above which can be operated in a reliable manner and at reasonable cost.
According to the invention, this object is achieved by arranging a pressure limiter between at least one of the pressure control units and the pressure regulator output, and, in the zero-current state, by limiting a supply hole for the at least one pressure control unit to a defined output pressure with the pressure limiter.
By means of the compressed-air processing system, it is advantageously possible to operate by means of different pressure levels for the safety-relevant brake pressure supply and the air suspension. In the energized operation of the compressed-air processing system, the various pressures are freely programmable and can be addressed individually by the operation or excitation of correspondingly provided solenoid valves. Thus, it is possible, for example, as a reaction to measured pressure values in the load circuits, with respect to pressure reduction, to charge in a targeted manner individual circuits at a sequence which can be defined by priorities. As a result, in a targeted manner, the charging of in each case only one circuit can also be provided which is then brought correspondingly faster to a desired pressure value. This ensures a fully electronic control of the compressed-air generating system which, furthermore, as a reaction to other measured values, such as coasting phases of the motor vehicle, overload of the compressor, or leakages in a certain circuit, can correspondingly separate individual circuits in order to return to a condition which is required for the safe operation of the motor vehicle. Likewise, as a reaction to detected humidity values in the compressed air and/or in an air dehydration cartridge, the control can trigger intermediate regenerations in a targeted manner in that, in the area of the air dryer cartridge, a flow reversal with already dried air is triggered in a targeted manner in order to regenerate the cartridge.
The control lines are expediently connected such with the valves triggering the regeneration that, during the energized operation, the pressure limiter is always held open. The supply hole for the circuits, which is arranged on the other side of the pressure limiter, and the pressure regulator output hole arranged on this side of the pressure limiter are then subjected to the same pressure, and the electronic control system determines, by defining the circuits to be charged, the supply of the compressed air to the circuits as well as the intermediate regenerations to be carried out. The intermediate regenerations are preferably triggered by the control for reasons of safety also after certain time intervals have elapsed.
In contrast, in the zero-current condition, after a preset value has been reached in the supply hole, the pressure limiter carries out an off-control and separates the supply hole from the pressure regulator output hole in the manner of a dynamic pressure stage. It therefore becomes possible, if an overflow valve of an air suspension is further developed correspondingly, which air suspension is connected with the pressure regulator output pipe, to first provide a pressure in the pressure regulator output hole which exceeds the switch-off pressure of the pressure limiter, and a higher pressure for the response of the overflow valve of the air suspension. This ensures that, even in the event of a failure of the electronic control, the safety relevant circuits are filled first. This also permits the further development of the air suspension without a separate air storage tank which reduces the cost of this component.
The compressed-air processing system according to the invention also advantageously permits the controlling of the pressure regulator also in the case of a limited circuit pressure which is still below the switch-off pressure. On the other hand, in the zero-current state, it is ensured by the response of the pressure limiter that, after the off-control pressure of preferably approximately 8.5 bar has been exceeded, no unlimited delivery takes place against the safety valve pressure. As a result, a compressor will reach the pressure regulator switch-off pressure more rapidly and can therefore be rendered inoperative correspondingly, which increases the life time of the compressor and reduces the energy consumption.
An electronic rapid switch-off possibility of the compressor is preferably also provided, for example, by way of a 3/2-way valve which, in the event of the electronically triggered regeneration is ventilated (or optionally magnetically excited) and is preferably also ventilated in the event of a pneumatic bleeding of the pressure regulator.
A solenoid valve for controlling the pressure regulator is expediently provided. The pressure regulator solenoid valve is preferably constructed as a 3/2-way valve and ventilates, when excited, a control line which, on the one hand, ventilates the pressure regulator such that the compressed air delivered by an air compressor is bled and, on the other hand, ventilates a piston of the pressure limiter such that this pressure limiter remains in its open position. In connection with the air bleeding of the pressure regulator, preferably a pneumatic 2/2-way valve is also ventilated which triggers the rapid switch-off of the air compressor delivering the inflowing compressed air. After the end of the excitation, a spring restores the solenoid valve of the pressure regulator, and the ventilated control line is bled and is therefore pressureless so that the pneumatic valves which follow in a cascade-type manner can also return into their starting position.
Furthermore, the compressed-air processing system advantageously comprises a solenoid regeneration valve which is constructed as a 3/2-way valve and triggers by excitation, on the one hand, a regeneration flow in the direction of an air dryer cartridge of the compressed-air processing system and, on the other hand, ventilates another piston of the pressure limiter and therefore fixes it in the open position. After the end of the excitation, a spring restores the solenoid valve of the pressure regulator and the ventilated control line is bled and thus becomes pressureless. It is understood that the solenoid regeneration valve can expediently be synchronized with the solenoid valve of the pressure regulator such that the solenoid regeneration valve will be excited only when the solenoid valve of the pressure regulator is also excited in order to permit the compressed air reversal in the air dryer cartridge. In contrast, the solenoid valve of the pressure regulator can also be controlled by the electronic control system without the necessity of a regeneration. It is possible to construct the two above-mentioned solenoid valves also in a common component, in which case only a synchronous pressure regulator ventilation/regeneration operation will then still be possible.
The compressed-air processing system preferably comprises a pilot valve for controlling the pressure regulator, which pilot valve responds independently of the electronic control system. As a threshold value for the response of the pilot valve, a pressure is expediently set by way of a preferably adjustable spring, in the case of which the control valve switches which is constructed as a pneumatic (mechanical) 3/2-way valve. When the preset pressure is exceeded, the pilot valve ventilates, by way of a control hole, the pressure regulator and carries out an off-control of the pressure regulator by bleeding. The control line preferably also controls a regeneration valve preferably constructed as a 2/2-way valve against its spring-loaded restoring force, whereby the regeneration of an air dryer cartridge can be triggered. According to a preferred construction, the regeneration valve is simultaneously constructed as a piston for the pushing-open of the pressure regulator which, at the end side, is ventilated by the control line and is simultaneously switched and displaced in order to rapidly and reliably synchronize the off-controlling of the pressure regulator and the regeneration of the air cartridge. The switch-off pressure of the pilot valve is expediently set higher than the switch-off values stored in the electronic control system, so that the pneumatic switch-off acts only as a backup position of the electronic switch off and does not undesirably interfere with the latter.
By means of the above-explained further developments of the invention, it is possible to fully electronically control the compressed-air processing system according to the invention and to nevertheless ensure the operational readiness in the event of the failure of the electronic system.
Additional characteristics and advantages of the invention are contained in the following description and in the subclaims.
The invention will be explained in the following by way of illustrated embodiments and with reference to the enclosed drawings.